It has long been a problem in public buildings, apartment houses and the like to equip common hallways, to which the public has access, with portable fire extinguishers in such manner that they will not be stolen. In addition, it has sometimes occurred that a portable fire extinguisher has been entirely, or partially, used to extinguish a fire and then replaced in its bracket with no alarm sounded and the fire not fully extinguished.
In an attempt to be sure that an alarm is sounded as soon as an extinguisher is removed from its holder, it has been proposed to enclose the extinguisher in a wall mounted box with a door, the opening of the door closing the alarm circuit, as in U.S. Pat. No. 3,042,910 to Shull of July 3, 1962.
Removing the weight of a fire extinguisher from its holder permits a spring plunger to rise and sound an alarm in U.S. Pat. No. 3,893,095 to Dejong of July 1, 1975 and both a door actuated switch and weight actuated switch are proposed in U.S. Pat. No. 4,015,250 to Fudge of Mar. 29, 1977.
However, the above devices, and other expedients are either too costly to manufacture or can be circumvented by a thief in slipping a cardboard, or screwdriver into the switch to hold it closed and than taping it while the extinguisher is removed without sounding the alarm.